1. Field of the Invention
The present invention relates to a rear wheel supporting system for a motorcycle and more particularly to a rear wheel supporting system for a motorcycle capable of preventing the occurrence of wobble.
2. Description of Relevant Art
In general, there occurs wobble (vibrations about a steering shaft) during a high-speed running of a motorcycle. It is known that wobble is influenced by dynamic characteristics of front and rear wheels, particularly of a rear wheel. It is also known that the variation in dynamic characteristics of front and rear wheels of a vehicle, especially of a rear wheel, does not affect the weave mode (vibration mode on a frequency of 4 Hz or so which varies with vehicular speeds) so greatly, but greatly affects the wobble mode (vibration mode at a frequency of 10 Hz or so which scarcely changes even if the vehicular speed changes).
On this regard, conventional rear wheel supporting systems for motorcycles comprise a rear fork whose front end of which is connected to a body frame vertically pivotably through a pivot shaft, a damper disposed between the rear fork and the body frame for supporting the rear fork in a suspended state, a wheel axle which is supported by the rear end of the rear fork, and a rear wheel mounted on the wheel axle so as to be rotatable integrally with a drive member such as a driven sprocket. The rear wheel has a freedom only in an arcuate direction around the pivot shaft of the rear fork. And this arcuate motion of the rear wheel is absorbed and cushioned by the damper.
In such construction of conventional rear wheel supporting systems, however, there inevitably occurs wobble during a high-speed running of the motorcycle, as previously noted, thus deteriorating the driving feeling in such a running condition.
The present invention has been accomplished for overcoming the above-mentioned problem of the conventional rear wheel supporting systems for motorcycles.
Particularly, the present invention is based on the consideration that vibrations of the rear wheel in the longitudinal direction of the vehicle body approximately perpendicular to vertical vibrations of the rear wheel which is to be absorbed by the damper are transmitted to the steering shaft through the rear fork and the vehicle body frame without being absorbed by the damper, thus resulting in the occurrence of wobble about the steering shaft.